Polishing system having a multi-phase polishing substrate and methods relating thereto

ABSTRACT

A chemical-mechanical polishing system which is particularly well suited for use in the manufacture of semiconductor devices or the like. The invention is directed to a polishing pad composition comprising a high modulus phase component and a low modulus phase component. The multi-phase polishing pads are very efficient and effective in providing high performance polishing along an entire polishing surface interface.

This application is a Continuation of U.S. application Ser. No.09/049,864 filed Mar. 27, 1998, now U.S. Pat. No. 6,099,394, which is aContinuation-in-Part of U.S. application Ser. No. 09/021,437 filed Feb.10, 1998, now U.S. Pat. No. 6,022,264, claiming the benefit of U.S.Provisional application Ser. No. 60/037,582 filed Feb. 10, 1997, andwhich claims the benefit of U.S. Provisional application Ser. No.60/042,115 filed Mar. 28, 1997, U.S. Ser. No. 60/041,844 filed Apr. 9,1997, and U.S. Ser. No. 60/064,875 filed Nov. 6, 1997. This applicationis a continuation-in-part of U.S. application Ser. No. 09/021,437 filedFeb. 10, 1998.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates generally to high performance polishingsystems for use in modifying a substrate by Hertzian indentation,fluid-based wear and/or any similar-type non-microgrinding mechanism;the polishing systems of the present invention are particularly wellsuited for use in the manufacture of semiconductor devices or the like.More particularly, the compositions and methods of the present inventionare directed to polishing systems comprising an aqueous based polishingfluid and a polishing pad; the polishing pads of the present inventioncomprise a polishing layer having two separate phases: a high modulusphase and a low modulus phase.

Definition of Terms

1. Polishing. “Polishing” is intended to mean chemical-mechanicalpolishing (as opposed to micro-grinding) and is intended to includeplanarization and any corresponding variations thereof The polishingsubstrates contemplated by the present invention include semiconductordevice substrates, such as, silicon, silica, gallium arsenide, siliconnitride, tungsten, tantalum, aluminum, copper, and any othersemiconductor device substrate, whether conducting, semi-conducting orinsulating.

2. Conditioning. In the art of chemical-mechanical polishing,conventional polishing pads generally must be conditioned or otherwiseroughened to initially create, then periodically renew, the pad'spolishing surface. Throughout this specification, “conditioning” isintended to mean mechanical and/or chemical surface treatment of a pad'spolishing surface to generate nanoasperities.

3. Nanoasperities. Throughout this specification, “nanoasperities” areintended to mean:

i. protrusions from the pad surface; and/or

ii. particles which release from the pad surface,

having an imputed radius (of curvature) of about 0.5 to about 0.1microns and sufficient resiliency to permanently deform (measured by thepermanent change in curvature during polishing) by less than 25%, morepreferably less than 10%.

4. Macro-Defects. Throughout this specification, “macro-defects” areintended to mean burrs or similar-type protrusions on the pad'spolishing surface of greater than 0.5 microns in any dimension.

5. Particles. For purposes of the present invention, “particle” isintended to mean a discrete mass of material as it exists at thepolishing interface. Hence, a “particle” can mean an independent,discrete primary particle, an agglomeration of primary particles whichform a discrete mass, and/or primary particles which are aggregatedtogether to form a discrete mass.

6. Self-dressing. Self-dressing is intended to mean that the polishinglayer abrades, dissolves, wears or otherwise diminishes during thepolishing operation, and as it diminishes, new nanoasperities are formedat the polishing interface, whether the pad is periodically conditionedduring its useful life or not.

7. Low modulus phase. “Low modulus phase” is intended to mean theportion of the polishing layer which is separate and distinct from thehigh modulus phase and which defines a modulus of less than about 10GigaPascals (“GPa”).

8. High modulus phase. “High modulus phase” is intended to mean aportion of the polishing layer which is separate and discrete from thelow modulus phase and which defines a modulus greater than about 10 GPa.The high modulus phase may further comprise a particle phase and anon-particle phase.

9. Pre-polymer. “Pre-polymer” is intended to mean any polymer precursor,including an oligomer, monomer, reactive polymer (includingcross-linkable or curable polymers) and/or the like.

DISCUSSION OF THE PRIOR ART

During chemical mechanical polishing, abrasive particles are generallyintended to be uniformly dispersed in a fluid along the entire polishinginterface. Ideally, as new slurry is pumped into the polishing interface(and old slurry moves out of the polishing interface), the abrasiveparticle distribution remains substantially uniform throughout thepolishing interface. With conventional polishing systems, such particledispersion uniformity (at the polishing interface) is very difficult toachieve, particularly during initial polishing (“start-up”).Non-uniformity of particles at the polishing interface generally lowerspolishing efficiency and performance.

Conventional polishing systems generally attempt to improve particleuniformity throughout the polishing interface by flowing large amountsof polishing slurries into the polishing interface and by using slurrieswith high loadings of abrasive particles. However with such conventionalpolishing systems, the substrate and polishing equipment generallyrequire extensive cleaning after the polish. This cleaning step slowsdown production, is prone to operator error and can create environmentalconcerns.

A need therefore exists in the art for a polishing system which providesimproved polishing uniformity along the polishing interface without theneed for flowing large amounts of polishing slurries (having highparticle loadings) into the polishing interface.

U.S. Pat. No. 5,435,816 to Spurgeon, et al, is directed to an abrasivearticle having a sheet-like structure for use in abrasion-type polishingof substrates.

SUMMARY OF THE INVENTION

The polishing systems of the present invention are directed to theplacing of a polishing fluid (which may or may not contain abrasiveparticles) between a polishing pad and a work-piece to be polished. Thepad comprises high modulus and low modulus domains which are exposed atthe polishing interface. The work-piece and pad are moved relative toone another, while at least a portion of the polishing fluid is locatedwithin the interface between the pad and work-piece. The movement of thepad and/or work-piece and the interaction of the polishing fluid combineto provide (chemical-mechanical) polishing.

Polishing in accordance with the present invention is directed to theremoval of surface protrusions by severing the chemical bonds betweenthe protrusion and the surface. This mechanism occurs at a molecularlevel and is much different from micro-grinding. Micro-grinding occurson a much larger scale, such as by surface fracturing, cutting orabrading.

Polishing pads in accordance with the present invention comprise apolishing layer created, at least in part, by solidifying a flowablematerial (including the sintering of flowable solids) into ahydrophilic, polishing layer matrix. Bonded within or onto the polishinglayer matrix is a high modulus phase. The low modulus phase of thepresent invention can be incorporated within or onto the polishing layermatrix and/or can be the polishing layer matrix itself.

The polishing fluid is preferably water based and may also comprisepolishing particles (in addition to any particles exposed by or releasedfrom the pad). The polishing fluid preferably comprises a pH modifierand optionally a pH buffer, surfactant, chelating agent, and/oroxidizer.

To provide consistency of polishing performance, any polishing pad flowchannel(s) should have a configuration whereby as the pad wears to onehalf the average depth of the largest flow channel, the amount ofsurface area capable of contacting the substrate changes by less than30%, more preferably less than 10% and most preferably less than 5%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged end sectional view showing a polishing pad inaccordance with the present invention.

FIG. 2 is a schematic side view of the polishing pad and polishingslurry of the present invention as used to planarize a substrate for usein the manufacture of a semiconductor device or the like.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) Overview

The present invention is directed to a single layer or multi-layerpolishing pad having a polishing layer containing at least a highmodulus phase and a low modulus phase (each phase being discrete andseparate from the other phase). Preferably, the weight ratio of the highmodulus phase to the low modulus phase is in the range of 0.00005:1 to10:1, more preferably 0.05:1 to 1:1.

The High Modulus Phase.

The high modulus phase can be a rigid organic, such as a thermoplastic,a rubber or a derivation thereof, or more preferably is a ceramic.Critical to the high modulus phase is that the modulus is greater thanabout 10 GPa. A preferred high modulus phase material is a ceramicparticle, particularly an oxide, most particularly a metal oxide. Highmodulus phase particles which may be incorporated into the polishinglayer material (and may also be incorporated into a polishing fluid), inaccordance with the present invention include:

1. alumina,

2. silicon carbide,

3. chromia,

4. alumina-zirconia,

5. silica,

6. diamond,

7. iron oxide,

8. ceria,

9. boron nitride,

10. boron carbide,

11. garnet,

12. zirconia,

13. magnesium oxide,

14. titanium dioxide, and

15. combinations thereof.

As used in this specification, “particle size” is intended to mean thedistance of the particle's largest dimension (either height, length orwidth). Preferred particles have an average particle size of less thanor equal to about 0.6 microns but preferably greater than or equal to0.05 microns; more preferably, at least 80 weight percent, morepreferably 95 weight percent, and yet more preferably 100 weightpercent, of the particles have a size in the range of 0.1 to 0.5microns.

In one embodiment, the high modulus phase comprises at least about 50weight percent, more preferably 80 weight percent and most preferablygreater than 95 weight percent particles having an average surface arearanging from about 25 square meters per gram to about 430 square metersper gram and an average diameter or average aggregate diameter of lessthan about 1 micron, more preferably less than about 0.6 microns.Preferred oxide particles of the present invention are alumina, silica,iron oxide, titania and ceria.

The surface area of the particles can be measured by the nitrogenadsorption method of S. Brunauer, P. H. Emmet and I. Teller, J. Am.Chemical Society, Volume 60, page 309 (1938) which is commonly referredto as BET measurement. Aggregate size can be determined by knowntechniques, such as, that described in ASTM D3849-89; measurements canbe recalled individually or in the form of statistical or histogramdistributions. Aggregate size distribution can be determined bytransmission electron microscopy (TEM) The mean aggregate diameter canbe determined by the average equivalent spherical diameter when usingTEM image analysis, i.e., based upon the cross-sectional area of theaggregate.

The Low Modulus Phase.

The polishing materials of the present invention have at least one lowmodulus phase that is sufficiently hydrophilic to provide a criticalsurface tension greater than or equal to 34 milliNewtons per meter, morepreferably greater than or equal to 37 and most preferably greater thanor equal to 40 milliNewtons per meter. Critical surface tension definesthe wettability of a solid surface by noting the lowest surface tensiona liquid can have and still exhibit a contact angle greater than zerodegrees on that solid. Thus, polymers with higher critical surfacetensions are more readily wet and are therefore more hydrophilic.Critical Surface Tension of common polymers are provided below:

Polymer Critical Surface Tension (mN/m) Polytetrafluoroethylene 19Polydimethylsiloxane 24 Silicone Rubber 24 Polybutadiene 31 Polyethylene31 Polystyrene 33 Polypropylene 34 Polyester 39-42 Polyacrylamide 35-40Polyvinyl alcohol 37 Polymethyl methacrylate 39 Polyvinyl chloride 39Polysulfone 41 Nylon 6 42 Polyurethane 45 Polycarbonate 45

In one embodiment, the low modulus phase is derived from at least:

1. an acrylated urethane;

2. an acrylated epoxy;

3. an ethylenically unsaturated organic compound having a carboxyl,benzyl, or amide functionality;

4. an aminoplast derivative having a pendant unsaturated carbonyl group;

5. an isocyanurate derivative having at least one pendant acrylategroup;

6. a vinyl ether,

7. a urethane

8. a polyacrylamide

9. an ethylene/ester copolymer or an acid derivative thereof;

10. a polyvinyl alcohol;

11. a polymethyl methacrylate;

12. a polysulfone;

13. an polyamide;

14. apolycarbonate;

15. a polyvinyl chloride;

16. an epoxy;

17. a copolymer of the above; or

18. a combination thereof.

Preferred low modulus phase materials comprise urethane, carbonate,amide, sulfone, vinyl chloride, acrylate, methacrylate, vinyl alcohol,ester or acrylaride moieties (most preferably, urethane). The lowmodulus phase material also defines a modulus of 1 Pa to about 10 GPa.Preferably at least one low modulus phase component of the presentinvention defines an elongation to break in the range of 25% to 1000%,more preferably 50%-500% and most preferably 100%-350%. The low modulusphase material can be porous or non-porous. In one embodiment, a lowmodulus phase component is non-porous; in another embodiment, a lowmodulus phase material is non-porous and free of fiber reinforcement.

Multi-Phase Material

A multiphase material of the preferred embodiment of the presentinvention is manufactured by mixing an aqueous dispersion of highmodulus phase material (or a precursor which can be converted into ahigh modulus phase material) with another phase (or a precursor toanother phase) material (the other phase material may or may not be alow modulus phase material). The other phase material is preferably apolymer based material, such as a thermoplastic or a thermoset.

In a preferred embodiment, the dispersion of high modulus material issubstantially free of particle agglomerations capable of scratching asemiconductor substrate. Particle agglomeration can be minimized byagitation or mixing of the dispersion shortly prior to intermixing themulti-phased material and solidifying (e.g., de-watering).

The low modulus material (or precursor thereto) can be 100% solids whenmixed with the dispersion of high modulus material (or precursorthereto), but in a more preferred embodiment, the low modulus materialis also a water based composition when mixed with the dispersion of highmodulus material (or precursor thereto). Once these two components areadequately mixed (substantially complete blending of the one componentwithin the other), the mixture is de-watered, such as by spray drying,oven drying or the like. As water is removed from the mixture, theresulting composition solidifies, with or without chemical reaction.Possible chemical reactions include curing, grafting, crosslinking,chain extension or the like.

In a highly preferred embodiment, an aqueous dispersion of submicronsilica particles is vigorously mixed into a urethane latex andde-watered by oven drying. The urethane component of the urethane latexcan be a polymer or in the alternative, can be a prepolymer which formsa final urethane polymer by a chemical reaction, such as by, chainextension, crosslinking or the like.

The multi-phased material comprises a high modulus phase in accordancewith the present invention. In some embodiments, the multiphasecomposition may also include low modulus phase material. Generally, thehigh modulus phase will be the continuous phase, and the other phase isthe discontinuous phase, but in alternative embodiments of the presentinvention, the continuous phase can be the high modulus phase.

The multiphase material can be formed into a polishing layer by casting,molding, skiving or other mechanical manipulation. In accordance withthe present invention, if the multi-phased material is formed into apolishing layer, the multi-phased material must also comprise a lowmodulus phase.

Alternatively, the multiphase material can be broken down into smallpieces, hereafter referred to as “clusters”, by milling or any otherparticle producing process. The multiphase clusters can then beincorporated into a conventional or non-conventional pad matrix materialto thereby provide a multiphase pad, whereby the multiphase component isin a particle format within a pad matrix. The pad matrix will generallybe yet another phase of material, and hence, such embodiments of thepresent invention will define more than two phases. Critical to thepresent invention is that the polishing pad have at least two phases—ahigh modulus phase (greater than about 10 GPa) and a separate lowmodulus phase (less than about 10 GPa). The pad (polishing layer) matrixcan be the same or different from either phase in the multi-phasematerial. In a preferred embodiment, the pad matrix and a phase of themulti-phase particulated material are generally different, but both arelow modulus phase materials.

A possible polishing layer matrix precursor is one capable of beingcured or polymerized via any appropriate polymerization mechanism, suchas substitution, addition or condensation polymerization reactions.Possible precursors include acrylated urethanes, acrylated epoxies,ethylenically unsaturated compounds, aminoplast derivatives havingpendant alpha, beta-unsaturated carbonyl groups, isocyanuratederivatives having at least one pendant acrylate group, isocyanatederivatives having at least one pendant acrylate group, and combinationsthereof.

Optionally, a diluent can be added to any phase of the present inventionto soften or otherwise lower the modulus of the material, thereby makingthe phase more prone to wear, to dissolving or to otherwise diminishingduring polishing. In one embodiment, the diluent is a polyol, such as,polyethylene glycol, methoxypolyethylene glycol, polypropylene glycol,polybutylene glycol, glycerol, polyvinyl alcohol, and combinationsthereof. In one embodiment, the diluent is polyethylene glycol having anaverage molecular weight of from 200 to 10,000 and comprising 20 to 60weight percent of the matrix material.

Optionally, an oxidizing component can be incorporated into the lowmodulus phase material to promote oxidation of a metal layer to itscorresponding oxide. For example, an oxidizing component can be used tooxidize tungsten to tungsten oxide; thereafter, the tungsten oxide canbe chemically and/or mechanically polished and removed. Preferredoxidizing components for incorporation into the low modulus phaseinclude oxidizing salts, oxidizing metal complexes, iron salts, such asnitrates, sulfates, potassium ferri-cyanide and the like, aluminumsalts, quaternary ammonium salts, phosphonium salts, peroxides,chlorates, perchlorates, pennanganates, persulfates and mixturesthereof. The amount should be sufficient to ensure rapid oxidation ofthe metal layer while balancing the mechanical and chemical polishingperformance of the system.

Other possible additives include fillers, fibers, lubricants, wettingagents, pigments, dyes, coupling agents, plasticizers, surfactants,dispersing agents and suspending agents. The polishing pad matrixmaterial can comprise up to 80 weight percent filler and other optionalingredients. Examples of optional additives include EDTA, citrates,polycarboxylic acids and the like. Although certain clays have beendescribed as being capable of acting as polishing particles, forpurposes of the present invention, the presence of clay materials withinthe low modulus phase are to be deemed as filler, not (high modulusphase) polishing particles.

Particle Clusters

High modulus phase materials, particularly sub-micron ceramic particlestend to agglomerate into much larger sized particles, and this can be aproblem, when creating the high modulus phase of the present invention.Such particle agglomeration can lead to scratching and can adverselyaffect polishing performance.

One way to avoid such unwanted agglomeration is to first: 1. mix theparticles with a suitable binder, whereby the binder is initially in aflowable form; 2. agitating or stirring the mixture to thereby break upparticle agglomerations and cause dispersion of the particles within theflowable binder; 3. Curing, de-watering or otherwise solidifying thebinder, thereby dispersing the particles within a (now) solid binder,and thereby also preventing the particles from re-agglomerating; and 4.grinding or otherwise breaking the resulting material into fragments.The resulting fragments will hereafter be referred to as “particleclusters.” The particle clusters are then incorporated into or bondedonto the polishing layer matrix material, and the particles are therebyincorporated into the polishing pad, substantially free of unwantedparticle agglomeration. The binder and/or the pad matrix can provide thelow modulus phase of the present invention.

The use of particle clusters is also advantageous, because it has beenfound that ceramic particles (without a binder) tend to weaken the pad'smechanical structure, due to poor adhesion between the particles and thepad matrix. Such decreased mechanical integrity is far less prevalentwith the use of particle clusters, particularly where a binder is chosenwhich is more compatible with or otherwise more effectively binds to thepad matrix.

The particle cluster binder material can be optimized for specificpolishing applications. The particle type, concentration anddistribution can be adjusted within the binder to further optimizepolishing performance for specific applications.

A Preferred Method of Fabricating Particle Clusters

According to one embodiment of the present invention, particle clustersare fabricated by mixing an aqueous dispersion of polishing particles,preferably colloidal, submicron metal oxide ceramic particles, with anaqueous dispersion of urethane prepolymer. The urethane (in either itsliquid pre-polymer state or its solid cured state) will hereafter bereferred to as the “intra-cluster binder.” The intra-cluster binder maybe, but is not limited to, urethane, epoxy, acrylic-urethane,polyacrylamide, polymethylmethacrylate, polyamide, polycarbonate,polyvinylalcohol and polysulfone.

Useful particles can include, but are not limited to, SiO₂, Al₂O₃, TiO₂and CeO₂. Particle sizes are preferably in the range of 10-1000 nm, morepreferably 30-500 nm and most preferably 50-300 nm. Preferredconcentrations of particles in the particle cluster are greater than 50weight percent, more preferably greater than 75 weight percent and mostpreferably above 90 weight percent.

The resulting particle/particle binder mixture is preferably dried toremove water. Drying techniques may include oven drying, evaporation,spray-drying, etc. The resulting material is ground or milled into afine powder, each granule of which constitutes a particle cluster.Grinding may be done by a mortar and pestle, roll mills, high-speedgrinders, or other similar means. In one embodiment, the material may beground into particle clusters ranging in size from 10-1000 μ(microns),preferably 25-500 μ, and more preferably 35-150 μ. The preferred size ofthe particle clusters will be governed by the size of the polishingparticles, the grinding method and the polishing application for whichthey are produced.

In some instances, where conditioning is not desired, it is advantageousto achieve compositions which are somewhat friable (e.g., crumble undershear forces, preferably of less than 1000 Newtons). Friability allows afresh supply of particles to be continuously introduced into thepolishing fluid. Friability is achieved by high filler loadings and/orby use of high glass transition temperature polymers (glass transitiontemperatures preferably greater than 25 degrees Centigrade). When fillerloadings are high, the particles are generally not fully surrounded bythe polymer, creating a relatively brittle material. High glasstransition temperature polymers tend to produce brittle matricesrendering the material relatively friable. Therefore, the rate ofintroduction of particles into the polishing fluid can be controlled byvarying the particle loading and the intra-cluster binder (e.g.,polymer).

Particle behavior during polishing is generally determined by how wellthe particles are held by the intra-cluster binder. The binder materialand the particles can be optimized for best polishing performance. Theconcentration and properties of the particles within the particlecluster can be changed independent of the bulk properties of thepolishing layer matrix. The size and concentration of the particleclusters within a polishing layer can also be varied to optimizeperformance.

Fabrication of Polishing Articles Containing Particle Clusters

In one embodiment of the present invention, particle clusters areincorporated into the polishing layer matrix by mixing the clusters intoa flowable polishing layer matrix precursor and solidifying the matrixby curing, cooling or any other solidification operation. Alternatively,the particle clusters are bonded to the polishing layer matrix, whilethe matrix is in a flowable or non-flowable state.

Useful manufacturing techniques may include, but are not limited to,molding, casting, extrusion, spray-coating, web-coating, printing,sintering, photopolymerization, or the like. Additional processing mayalso be incorporated into the polishing pad manufacturing process, suchas grooving, skiving, felting and foaming or the like. Grooving isintended to mean producing recesses of any shape on the article'spolishing surface.

In one embodiment of the present invention, the polishing layer matrix(prior to solidification) with particle clusters dispersed therein iscoagulated or otherwise coated and solidified upon a substrate, such asa felt or polymer film. Coagulation can form a porous,particle-containing material.

The particle clusters can be dispersed in liquid urethane precursorsused in existing processes for the manufacture of polishing articles.The loading of particle clusters may be in the range of 1-95 weightpercent. More preferably the particle loading is in the range of 10-90and most preferably in the range of 25-85 weight percent. Theconcentration of the particle clusters can be varied over a wide rangeto achieve desired characteristics for different applications. Forinstance, high loading increases friability. Compositions preventingparticle cluster agglomeration allow uniform distribution to beachieved.

The particle clusters should not interact chemically with the bulkconstituents of the article in ways that would inhibit theirperformance. However, the inter-cluster polymeric matrix chemistry maybe adjusted to obtain desired behavior of the particle clusters withinthe matrix. For instance, adjustments to the inter-cluster polymerchemistry may allow the particle clusters to attach to a surface of thearticle instead of being distributed evenly throughout.

In one embodiment the mixture of particle clusters in the inter-clusterpolymeric matrix is transferred to a mold. The mixture is allowed to geland then cured at elevated temperatures. The solidified cake is broughtto room temperature and removed from the mold. The cake is skived, orsimilarly sectioned, to form polishing articles of desired thickness'.The articles may be used in this form or layered with other articlessuch as foams depending on the application. The top layers may beperforated or grooved.

In an alternative embodiment particle clusters may be dispersed in awater soluble polymer to allow release of particle clusters into anaqueous polishing fluid during use. Examples of such polymers include,but are not limited to, polyvinylalcohol or polyacrylamide.

Particle clusters may be mixed with an inter-cluster polymeric binder,preferably an aqueous dispersible polymer, then sprayed onto a substrateto form a polishing article. The preferred loading of particle clustersmay be 5-95 weight percent, more preferably 20-90 weight percent, andmost preferably 40-85 weight percent. The mechanical integrity of asprayed article is dictated by the substrate. Therefore, the particlecluster loading can be higher in sprayed mixtures than in matrices thatform an entire polishing article (or polishing article layer for acomposite article). The substrate may be any material possessing theflexibility, elasticity and other properties necessary for successfulpolishing. The inter-cluster polymeric binder and substrate must havesufficient adherence to one another so that the particle clustersrelease the polishing particles more readily than the substrate releasesthe binder.

Particle clusters may be sprayed in layers. Each layer is dried andeither totally or partially cured before application of subsequentlayers. Preferably surfactants are added to the inter-cluster binder toenhance adhesion between layers. Layering serves to increase thethickness of the article, thereby increasing longevity. Layering alsoprovides a means to vary the polishing capabilities within a singlearticle. For example, layers may vary in particle size, type or loading,or in particle cluster type, size or loading. Also a single layer maycontain different types, sizes or concentrations of particle clusters.

The rate of particle release into the polishing fluid can be controlledby varying the particle loading of the cluster, the particle clusterloading of the material, or by varying the types and ratios of all othermaterials comprising the clusters and polishing layer matrix.

In one embodiment of the present invention, particle clusters are mixedgradually into a reactive precursor to the polishing layer matrix. Onceformed, the polishing layer matrix will comprise the low modulus phaseand the particle clusters (which comprise a high modulus phase) aredispersed within the matrix. Examples of suitable mixing techniquesinclude low shear and high shear mixing; high shear mixing beingpreferred. Ultrasonic energy may also be utilized in combination withthe mixing step to lower the dispersion viscosity. The amount of airbubbles in the dispersion can be minimized by pulling a vacuum during orafter the mixing step. In some instances, it may be preferred to addheat during mixing, generally in the range of 30 to 70 degreesCentigrade, to lower viscosity. The dispersion should have a rheologythat coats well and in which the particles and other fillers do notsettle.

A preferred matrix precursor material comprises a free radical curablecomponent. Such polymerization can generally be initiated upon exposureto thermal or electromagnetic energy, depending upon the free radicalinitiator chemistry used. The amount of energy necessary to inducepolymerization depends upon several factors such as the binder precursorchemistry, the dimensions of the matrix precursor material, the amountand type of particles and the amount and type of optional additives.Possible radiation energy sources include electron beam, ultravioletlight or visible light. Electron beam radiation, which is also known asionizing radiation can be used at an energy level of about 0.1 to about10 Mrad, preferably within the range of about 250-400 nanometers.

Also preferred is visible light radiation in the range of about 118 to236 Watts per centimeter; visible radiation refers to non-particulateradiation having a wavelength within the range of about 400 to about 800nanometers, preferably in the range of about 400 to 550 nanometers. Itis also possible to use thermal energy to initiate the free radicalpolymerization, provided the polymerization chemistry is adaptable tothermally induced free radical initiation and curing.

In a preferred embodiment, the resulting mixture (of low modulus phase,polishing layer matrix precursor, particle clusters and optionalingredients, if any) is then applied to a substrate as the precursor issolidified (e.g., polymerized) to create a polishing layer comprising ahigh modulus phase (found within the clusters) and a low modulus phase(the polishing layer matrix and/or a second phase within the cluster).The substrate upon which the mixture is applied can be left bonded tothe mixture to form a multilayer pad. In such an embodiment, thepolymerization reaction should induce adhesion between the substrate andmatrix material, and the substrate should be prone to surface wetting bythe precursor matrix material.

In an alternative embodiment, the solidified mixture is peeled away fromthe substrate (such as a mold) to form a monolayer. This monolayer canbe used as a pad or additional layers can be applied to the monolayer toprovide a multilayered pad. Regardless of whether the final pad is amonolayer or multilayer, the multi-phased material will define at leastone polishing surface of the pad.

The pad layer (pad matrix containing particle clusters) can be partiallyor wholly solidified upon a belt, a sheet, a web, a coating roll (suchas a rotogravure roll, a sleeve mounted roll) or a die. The substratecan be composed of metal (e.g., nickel), metal alloys, ceramic orplastic. The substrate may contain a release coating (e.g., afluoropolymer) to permit easier release of the cured material from thesubstrate.

The partial or complete solidification of the polishing layer can occurwith the mixture in contact with a mold or other means to induce a threedimensional pattern upon a surface of the mixture. Alternatively, thesurface of the mixture can be modified by any available technique, suchas, photolithography and/or machining. In yet another alternativeembodiment, the matrix surface is not modified, but rather, the surfacetexture remains as was naturally produced when hardening (e.g.polymerizing) the precursor to provide the solid matrix material.

Flow Channels

Conventional polishing pads generally perform better with a series oflarge and small flow channels. In a preferred embodiment of the presentinvention, the flow channels continuously evolve (some are created asothers diminish), as the multi-phase material abrades, dissolves orotherwise diminishes.

To provide consistency of polishing performance, any flow channel(s)should have a configuration (such as rods or cylinders perpendicular tothe pad's surface) whereby as the pad wears to one half the averagedepth of the largest flow channel, the amount of surface area capable ofcontacting the substrate changes by less than 25%, more preferably lessthan 15% and most preferably less than 10%. In one embodiment,substantially all flow channels define a groove having a width whichvaries by no more than 20% (more preferably no more than 10%) betweenthe top and bottom of the groove.

In another embodiment, pads in accordance with the present inventionhave a pyramidal, truncated pyramidal or other three dimensional surfacetexture, whereby the polishing surface area will tend to change as thepad wears. To offset variations in polishing surface area during theuseful life of the pad, the downward pressure upon the pad is adjustedto maintain a substantially constant frictional resistance between thepad and substrate.

Pad Longevity and “Self-Dressing”

High loadings of the high modulus phase will generally decrease padlife, since high loadings of the high modulus phase material will tendto release rigid domains and as these domains are released, the padwears away. However such high loadings of the high modulus phase can beadvantageous, because the release of high modulus domains renews thepolishing surface of the polishing layer and thereby can decrease theamount of conditioning necessary during the life of the pad.

Such a decrease in pad conditioning is advantageous, becauseconditioning slows production, is labor intensive and presents anopportunity for operator error. The high modulus phase can be adjustedto fine tune the release of high modulus domains (e.g., particles),thereby influencing the amount of pad conditioning required during thepad's useful life.

Alternatively, by decreasing the high modulus domain loading, thepolishing layer can become less friable, and this generally improves thepad's mechanical integrity and generally increases the pad's servicelife. Generally speaking, high modulus phase loadings above 50wt % tendto decrease the need for pad re-conditioning.

Recess-Filled Polishing Articles

In one embodiment of the present invention, an indentation (such as agroove) is incorporated into the polishing layer surface. Theindentation is then filed with a filler comprising high modulus phasematerial. For example, a conventional polyurethane pad can be machinedto form grooves on the polishing surface. The polyurethane pad matrixcan comprise low modulus phase material and can be devoid of highmodulus phase material. The grooves can then be filled with acomposition comprising high modulus phase material. Once theindentations are filled (such as by spraying), the overall surface ofthe pad can be substantially planar. By controlling the geometry of thegrooves, especially the width and by adjusting the density of the highmodulus material within the recess, it is possible to equalize the wearrates of the pad and the filler within the indentation(s). In this way,the underlying pad can provide mechanical integrity and the filledgrooves can act as a continuous source of nanoasperities.

Sintered Polishing Pads Containing Particle Clusters

In accordance with the present invention, polishing articles (comprisingboth a high modulus phase and a low modulus phase and containingparticle clusters) may be fabricated by a sintering process. In apreferred embodiment, the process begins by mixing the particle clusterswith low modulus phase material capable of being sintered.Concentrations of the low modulus phase can range from 5 to 95 weightpercent, preferably from 20 to 90 weight percent, and more preferablyfrom 40 to 85 weight percent, depending upon the concentration ofparticles in the clusters and the desired loading in the polishingarticle. As the concentration of particle clusters increases, thefriability of the polishing material tends to also increase.

Low modulus phase materials preferably sinter at temperatures andpressures below the decomposition temperature/pressure of the selectedparticle clusters. Nylon is a low modulus phase material which is oftensuitable for sintering polishing pads of the present invention. Otherpossible low modulus phase materials which may also be suitable forsintering include: thermoplastic polyurethanes, polyvinyl chloride,polycarbonate, polymethylmethacrylate, polysulfone and combinationsthereof.

In the preferred embodiment, once a dispersion of particle clusterswithin the low modulus phase material is achieved, the mixture is pouredinto a mold and heated for sufficient time and temperature to fuse thestructure together. By varying the temperature, time and pressure,different degrees of sintering can be achieved. At one extreme, a fullydense material can be sintered with no residual porosity and with highmechanical strength. Alternatively with partial sintering, the resultingmaterial generally has open channels and is often porous and friable, atleast to some degree. Thus, the degree of sintering can be used as yetanother way of controlling the friability, including the propensity forreleasing (high modulus) particles. This unique characteristic of thepresent invention generally reduces or eliminates the need for articleconditioning by continually generating a fresh article surface duringpolishing.

The mold used can contain grooves or any other shaped designs, thepattern of which under the process of molding produces recesses in thearticle. Recesses may also be incorporated into the article after itsformation by methods such as embossing or the like.

Other methods of producing sintered articles include, but are notlimited to, wet forming, powder compaction and electrophoreticdeposition.

EXAMPLES

The present invention includes a method for polishing comprising thesteps of: 1) formulating a polishing article having particle clustersincorporated therein; 2) introducing a polishing fluid, preferablycontaining little or no particulate material, between the article and aworkpiece to be polished; and 3) producing relative motion between thearticle and workpiece. Following are examples further describing thearticles and methods of the present invention. They are not intended tobe restrictive in any way.

Example 1

This example describes one embodiment of particle cluster fabricationaccording to the present invention. A formulation was prepared having 5weight percent A-100* and 95 weight percent CeO₂**. A 1935 g CeO₂aqueous dispersion (the concentration of CeO₂ in the dispersion was21.5%) was prepared and poured into a mixer. Using high shear mixing, 63g of an aqueous dispersion of A-100 (concentration of 55%) was slowlyadded to the CeO₂ dispersion. Mixing continued for 30 min. The resultingmixture was poured into an aluminum pan and heated for fourteen hours at60° C. until dried The dried mixture was ground by mortar and pestle toa fine powder. Each grain of powder represented a particle cluster.

*A-100—a water based colloidal dispersion of urethane and polyacrylatecopolymer manufactured by Witco, Inc.

**CeO₂—water dispersion with a primary particle size of 200 nm,manufactured by Mitsui Chemical Company.

Example 2

This example describes a dispersion of particle clusters in aninter-cluster polymer.

TABLE 2 Weight Percent of Cluster/Interpolymeric Binder FormulationW-242^({circle around (x)}) 52.4 Particle Clusters 27.5 (as prepared inexample 1) XW^({circle around (x)}{circle around (x)}) 1.0 VelvetexBK-35^({circle around (x)}{circle around (x)}{circle around (x)}) 1.6Deionized water 17.5 ^({circle around (x)})W-242 urethane aqueousdispersion manufactured by Witco, Inc.^({circle around (x)}{circle around (x)})XW epoxy aqueous dispersionmanufactured by Witco, Inc.^({circle around (x)}{circle around (x)}{circle around (x)})VelvetexBK-35 surfactant manufactured by Henkel Corporation

Three-hundred grams of a W-242 aqueous dispersion, 157.5 g of particleclusters produced as in Example 1, 6.0 g of XW, 9.0 g of surfactant and100 g deionized water were mixed in a laboratory jar-mill (with zirconiaas a ball-mill medium) for fourteen hours. A spray-gun was used to spraythe mixture on the surface of a grooved IC-1400 pad (polishing padmanufactured by Rodel, Inc., Newark, Del.). After spraying, the pad washeated in an oven at 60° C. for fourteen hours.

Example 3

This example describes one embodiment for a method of polishing. Thermaloxide wafers were polished using a polishing pad prepared in Example 2.The pad was mounted on a Strasbaugh 6CA polishing machine platen. Thepad was rinsed with de-ionized water and conditioned with 200 gritdiamond grid for 3 min. A particle-free polishing slurry (NH₄OH (1.7%)in water) was introduced on the surface of the pad at a rate of 100ml/min. A platen speed of 60rpm and a quill speed of 50 rpm were used.The pressure between the pad and the wafer was 8 psi. The wafer waspolishing for 2 min. then rinsed with de-ionized water for 30 seconds.Seventy-five thermal oxide wafers were polished with one pad. There wasno reconditioning between wafers. An average removal rate of 3000-3500Å/min was achieved.

Pad Plus Slurry.

The polishing systems of the present invention comprise the (abovedescribed) polishing pad design in combination with a polishing slurry.Any particle containing polishing fluid can be used. Preferred polishingslurries comprise less than 95 weight percent particles, more preferablyless than 40 weight percent particles, more preferably less than 25weight percent particles and most preferably 0-10 weight percentparticles. In one embodiment, the polishing fluid comprises an amine,polyol, carboxylic acid, halogen ion and/or oxidizing agent.

During polishing, preferred polishing fluids provide increasedreactivity or corrosivity at the point of particle contact orinteraction with a surface protrusion. For example, if the polishingfluid is more corrosive at higher temperatures, then corrosion willpreferentially occur at this point of contact, since the temperature atthe point of contact is generally higher than at non-contact portions ofthe surface. A particularly preferred polishing fluid provides acorrosion rate which increases as the protrusion is stressed (i.e., bondstrain is induced) due to particle contact or interaction.

Dilute solutions of hydrofluoric acid are corrosive to SiO₂ and silicatematerials. The rate of corrosion is sensitive to bond strain,particularly tensile strain. The corrosion rate increases by more thanan order of magnitude. Such a reactive solution when used in accordancewith the polishing pads of the present invention will generally resultin a highly selective local removal in the proximal vicinity of theparticle contact, due to the increased local bond strain in thesubstrate.

A preferred polishing slurry of the present invention for use in thepolishing of silicon is a water based slurry, comprising about 0.05 toabout 5 weight percent amine, preferably primary amine capable ofreceiving a free proton. In addition or in the alternative to the aminethe following can be used: a halogen ion, particularly a fluoride ion; ahydroxyl ion; and/or a superoxide, such as peroxide, persulfate,permagnate or the like. A preferred pH for the polishing fluid of thisembodiment is in the range of about 2-12.

Recycle of Polishing Fluid

In another embodiment, the polishing fluid is recycled back into thepolishing operation. Prior to re-use, the polishing fluid can befiltered or otherwise processed or rejuvenated. If the slurry comprisesa dilute hydrofluoric acid solution, the pH and HF concentration may bemeasured in situ before and after use. Provisions for additional HF intothe slurry as needed to maintain a constant acid concentration and pHcan be introduced into the recirculation system.

Similarly, for a slurry comprising 50 parts per million ozone in waterat pH 4, the oxidation potential of the solution (which is directlyproportional to the ozone concentration), and the pH may be measuredwith conventional electrodes; acid and ozone can then be added duringthe recirculation process to maintain consistency in polishing fluidperformance.

Referring now to the drawings, FIG. 1 is an enlarged sectional viewshowing a polishing pad in accordance with the present invention. Thepad 10 comprises a polishing surface 12 comprising a low modulus phasematerial 14 having high modulus phase particles 16. Optional flowchannels are shown at 18 and 20. FIG. 2 provides a schematicrepresentation of a polishing process in accordance with the presentinvention. The polishing apparatus is shown generally at 100, comprisinga table 102, workpiece 106 and polishing pad 104. Polishing fluid ispumped into the polishing interface (between the pad and workpiece) byinfluent line 105. Used polishing fluid exits the polishing apparatusvia effluent line 108. The used polishing fluid is filtered by filter110, and deionized by ion exchange column 112. Excess polishing fluidcan be removed by waste line 114. Sensor 116 then monitors the pH orother chemical properties of the recycled fluid, and inlet line 120provides appropriate additives to the recycled fluid, therebyrejuvenating it for another polishing cycle. Sensor 122 monitors thepolishing fluid entering the polishing operation to ensure proper pH orother properties which are desired to be monitored for quality control.

Nothing from the above discussion is intended to be a limitation of anykind with respect to the present invention. All limitations to thepresent invention are intended to be found only in the claims, asprovided below.

What is claimed is:
 1. A polishing system for use in polishing asemiconductor device substrate at a polishing interface between thesubstrate and a polishing pad, comprising: a polishing pad having apolishing layer comprising a high modulus phase component and a lowmodulus phase component, the low modulus phase component having acritical surface tension greater than or equal to 34 milliNewtons permeter and a modulus less than about 10 GPa, the high modulus phasecomponent having a modulus greater than about 10 GPa, the high modulusphase component comprising a plurality of ceramic particles having anaverage diameter of less than 1 micron, the polishing layer beingsubject to wear during polishing of the substrate, whereby as thesurface of the polishing layer wears during said polishing of thesubstrate, nanoasperities are created at the polishing interface duringsaid polishing, by at least a portion of the high modulus phasecomponent being provided at the polishing interface, either asprotrusions from said surface, or by being released from said surface tothe polishing interface; and an aqueous polishing fluid located at thepolishing interface, the aqueous polishing fluid comprising 0-50 weightpercent abrasive particles having an average diameter of less than 1micron.
 2. A polishing system in accordance with claim 1 wherein thepolishing fluid comprises a pH modifier, the low modulus phase componenthas a modulus of less than 1 GPa, and the high modulus phase componenthas a modulus of greater than 10 GPa.
 3. A polishing system inaccordance with claim 1, wherein the polishing fluid comprises less than20 weight percent abrasive particles.
 4. A polishing system inaccordance with claim 1, wherein the polishing fluid comprises less than5 weight percent abrasive particles.
 5. A polishing system in accordancewith claim 1 wherein the high modulus phase component comprises ceramicparticles having an average particle size in the range of 0.1 to 0.4microns, at least 50 weight percent of said particles being alumina,silica, ceria, or a combination thereof, and the weight ratio of saidparticles to the low modulus phase component is in the range of 0.0001:1to 5:1.
 6. A polishing pad for polishing a substrate, comprising: apolishing layer comprising a high modulus phase component and a lowmodulus phase component, the low modulus phase component having acritical surface tension greater than or equal to 34 milliNewtons permeter and a modulus less than about 10 GPa, the high modulus phasecomponent having a modulus greater than about 10 GPa, the high modulusphase component comprising a plurality of ceramic particles having anaverage diameter of less than 1 micron, whereby as the polishing layerwears during said polishing at a polishing interface between thepolishing layer and the substrate, nanoasperities are created by atleast a portion of the high modulus phase component being provided atthe polishing interface, either as protrusions from said surface, or bybeing released from said surface to the polishing interface.
 7. Apolishing pad in accordance with claim 6, further comprising a pluralityof particle clusters held by the polishing layer, said particle clusterscontaining the high modulus phase component and a different materialthat provides a phase which is separate and distinct from the highmodulus phase of the high modulus phase component, said particleclusters having an average size in the range of 10 to 1000 microns.
 8. Apolishing pad in accordance with claim 7, wherein the particle clustershave an average size in the range of 25-500 microns.
 9. A polishing padin accordance with claim 6 further comprising at least one groove, atleast a portion of said high modulus phase component being locatedwithin said groove.
 10. A polishing pad in accordance with claim 6,wherein at least a portion of the low modulus phase component issintered.
 11. A polishing pad in accordance with claim 6, wherein atleast a portion of the high modulus phase component is adhered to asurface of the polishing layer.
 12. A polishing pad in accordance withclaim 6, wherein the polishing layer has a surface texture comprising anon-random pattern.
 13. A polishing system using a polishing pad forpolishing a semiconductor device substrate at a polishing interfacebetween the substrate and said polishing pad, comprising: an aqueouspolishing fluid comprising 0-50 weight percent abrasive particles havingan average diameter of less than 1 micron; and said aqueous polishingfluid being adapted for use with said polishing pad having a polishinglayer comprising a high modulus phase component and a low modulus phasecomponent, the low modulus phase component having a critical surfacetension greater than or equal to 34 milliNewtons per meter and a modulusless than about 10 GPa, the high modulus phase component having amodulus greater than about 10 GPa, the high modulus phase componentcomprising a plurality of ceramic particles having an average diameterof less than 1 micron, the polishing layer being subject to wear duringpolishing of the substrate, whereby as the surface of the polishinglayer wears during said polishing of the substrate, nanoasperities arecreated at the polishing interface, by at least a portion of the highmodulus phase component being provided at the polishing interface,either as protrusions from said surface, or by being released from saidsurface to the polishing interface.
 14. A polishing system using anaqueous polishing fluid for polishing a semiconductor device substrateat a polishing interface, comprising: a polishing pad having a polishinglayer comprising a high modulus phase component and a low modulus phasecomponent, the low modulus phase component having a critical surfacetension greater than or equal to 34 milliNewtons per meter and a modulusless than about 10 GPa, the high modulus phase component having amodulus greater than about 10 GPa, the high modulus phase componentcomprising a plurality of ceramic particles having an average diameterof less than 1 micron, the polishing layer being subject to wear duringpolishing of the substrate, whereby as the surface of the polishinglayer wears during said polishing of the substrate, nanoasperities arecreated at the polishing interface that is between the substrate and thepolishing pad, the nanoasperities being created by at least a portion ofthe high modulus phase component being provided at the polishinginterface, either as protrusions from said surface, or by being releasedfrom said surface to the polishing interface; and the polishing padbeing adapted for use with said aqueous polishing fluid comprising 0-50weight percent abrasive particles having an average diameter of lessthan 1 micron.